STS stands for "Space Transportation System." In the aerospace industry, STS refers to the Space Shuttle, which was a reusable spacecraft that was used by NASA for over 30 years to carry astronauts, payloads, and supplies to and from low Earth orbit.
The Space Shuttle was composed of several main components, including the orbiter (the main crew and payload vehicle), the solid rocket boosters (SRBs), and the external fuel tank (ET). The orbiter was the main component of the Space Shuttle and was the only reusable part of the system. It was designed to carry a crew of up to seven astronauts and could carry a variety of payloads, including satellites, the International Space Station (ISS) modules, and scientific instruments.
The Space Shuttle was launched vertically like a rocket, and it was powered by the SRBs and the main engines of the orbiter. The SRBs provided the majority of the thrust needed to lift the Space Shuttle off the launch pad and into orbit, while the main engines of the orbiter provided the additional thrust needed to reach orbital velocity. The ET supplied the fuel for the SRBs and the main engines of the orbiter.
The Space Shuttle was retired in 2011, and it has been replaced by other spacecraft for NASA's manned spaceflight missions.